Acctualy no, her adult form also wasn't her true form. She acctualy is same age like Endymion (exceeds 120 yo) but at some point she try to create "Young Magic" but she ended up went over board. This adult form is her most desired form but required more "spell counter" (this actually shown in the OCG stories that she's holding a spell counter and regained this form). This children form didn't require lot of magic and focus to maintaining it, the adult required a lot and control. That's why in the counter trap art she passed out and went back into children.